I have an axle from a '97 Expedition 4WD (loved it before it was totaled) with 9.75-3.73 gears and a LS diff. I was going to swap it with my current '97 F150 2WD axle with 9.75-3.55's, open diff. and rear drum brakes. Problem is, the Exp. axle has the bottom airbag mounts instead of shock and leaf spring mounts and has disc brakes (a plus) but this means there will most likely be welding involved (which I cannot do) to try and install my shocks and leaf springs. I went from the factory tire size of 245/75/16's to my current 265/70/17s. I've read some previous posts re: 3.55 to 3.73 gear swaps and have gotten mixed reviews, some good some bad (only 5% difference, blah, blah, blah, etc). I'd like to do some light mud playing and the heaviest thing I'd be towing around is my '69 camaro (yeah, yeah I know...chevy..). Bottom line: is it worth it to do the axle swap (or maybe just gear swap, I'd really like to have the LS)? Of course I'd like a better launch from stop and better fuel econ., but I'm just not sure if its worth it. I've got the parts but should I blow the dough to have it done or not bother with it. Can anybody nudge me to either side? Thanks in advance for your help!

 

Is it really worth the time and effort to modify the Expedition axle to fit when there is an over-abundance of F-150 rear ends in salvage yards all across the country? Weigh the option of paying someone to cut the old mounts off, grind the axle down, weld the new perches in place (which they may need to fabricate), and in order to do all that, most shops will require you remove the guts (may as well rebuild it at that point), and there's no guarantees that the axle will be straight when they get done, not to mention they'll need ot be sure they get the pinion angle correct which can be a craps-shoot at best.

For the same price as all that labor, you can likely pick a relatively low-mile F-150 axle out of a junkyard with the same gear ratio and the same (IMHO useless) Ford trac-loc limited slip. Heck, for that matter, get an open diff and drop in a true limited slip like a Torsen or a Detroit Truetrac. You'll be much happier.... have the shop set up the limited slip, then all you have to do is two u-bolts on each side, one ABS connector, and a brake hose. Bleed the brakes and you're back on the road!

Just my .02....

-Joe

 

IMO Stick with what you have, Why put time and money into a rear end that might save you .5 MPG on the freeway. Just my .02

 

If you're wanting to swaps gears or axles or whatever, I'd say do it right the first time and don't screw around with it - get a real limited slip or locking differential, a new ring and pinion set and all the bearings and have it set up.

It'll cost a lot more, but you won't likely ever have to worry about the axle again.

 

I find that 3.55 gears with a 265/75/16 are perfect for towing cars. In 3rd gear the rpm's are about 2700 at 65mph. If I recall correctly the rpm's were about 3000 with the 245/75/16 at the same speed. I guess the 3.73 gears should be about 200 rpm faster than the above numbers. Also, I've always felt that gear swaps were only worth it if you went 2 gears up ( 3.90 ish in your case). You really shouldn't notice much of a differance between 3.55 and 3.73 daily driving in my oppinion.